The physiological modification of molecules and supramolecular assemblies plays a major role in the structure and regulation of biological systems. These modifications may include “local” modifications, such as phosphorylation, cyclization, prenylation, carboxylation, glycosylation, acylation, and/or sulfonation of amino acids, nucleotides, and/or lipids, among others, as well as the reversal of these modifications. These modifications also may include “global” modifications, among others, such as cleavage and/or ligation of proteins, nucleic acids, and/or lipids, in which molecules are split into two or more fragments or spliced to one or more other molecules, respectively.
The prevalence and significance of molecular modifications make it particularly likely that errors in modifications and/or errors in the regulation of such modifications will lead to disease and/or other pathologies. Therefore, there is intense interest both in characterizing molecular modifications and in understanding their regulation. There also is intense interest in identifying and/or characterizing activating and/or inhibitory drugs to modulate molecular modifications. This interest, in turn, has created a demand for assays of molecular modifications and/or their effects. Unfortunately, standard assays have a number of shortcomings, including the use of radioactive labels (with their attendant safety issues), binding partners that are excessively specific to the substrate or product (making them difficult to use with more than one or unknown substrates or products), and/or slow time courses and unstable endpoints (that require precise timing of assay readouts), among others. Thus, there is a significant need for molecular modification assays that are both safe and simple.